Three classes of components are important in oxidative hair dyeing: oxidation dye precursors, oxidants, and couplers.
The oxidation dye precursor can be a primary intermediate such as a difunctional benzene derivative capable of being oxidized with resultant development of color, e.g. ortho- and para-phenylenediamines and para-aminophenols, or a hydroxyindole such as 5,6-dihydroxyindole.
Hydrogen peroxide is the usual oxidant, although persalts of various acids or solid organic peroxide adducts may be employed, especially where a solid oxidant is desired.
The third component type-the coupler-is important in hair coloring to produce color nuances necessary for the simulation of a natural hair color.
It is well known that the shade or color produced by a color coupler depends on its chemical nature.
The production of red shades has always been a problem in the development of lines of oxidative hair colorants. This was due to the absence of true "red couplers" among the various dye precursors. The problem was first overcome by the use of direct dyes in admixture with the oxidative dye precursors. In particular, 2,5-diaminonitrobenzene was widely used for this purpose. Moreover, the red direct dyes exhibit very poor wash fastness particularly on hair which had been previously subjected to permanent waving or relaxing. In consequence, the red shades so produced rapidly become drab brown after as little as one or two shampooings.
An attempt to improve the lastingness of red shades was the subject of U.S. Pat. No. 3,210,252 which disclosed the use of p-aminophenol and 5-amino-2-methylphenol and of U.S. Pat. No. 4,065,255 directed to the use of p-aminophenol and 5-(.beta.-hydroxyethyl) amino-2-methylphenol to produce red shades by an oxidative method. While these couples represent an improvement over the use of direct dyes, they still suffer from less than optimal light and wash fastness in oxidative dye compositions.
Furthermore, these couples produce an orange-red when coupled with p-aminophenol and a magenta when coupled with p-phenylenediamine and, when used in combination with both p-aminophenol and p-phenylenediamine, a dull hue is obtained.
Moreover, in alkaline dyeing formulations the couples are actually a vivid violet color due to ionization of the phenolic group. It is only after shampooing and the consequent drop in pH that the red color is evident. This has a very disconcerting effect on the dye user, as evidenced by calls to the manufacturers from consumers and hairdressers.
A second method to produce red shades involves the coupling of 1-naphthol and p-aminophenols as disclosed in U.S. Pat. Nos. 4,169,703, 4,997,451 and 5,047,066. This coupler is typically used to produce strong blue colors by coupling with p-phenylenediamines (U.S. Pat. No. 3,970,423). The red color produced is a weak orange-red as disclosed in the above patents and it is only poorly stable to light and shampooing. In view of these problems, it is not widely used.
The present inventors have surprisingly found that, when reacted with an oxidation dye precursor in the presence of a suitable oxidant, 2-substituted-1-naphthols of the general formula I ##STR1## or salts thereof, preferably the sodium salt, wherein R is C.sub.1 -C.sub.6 alkyl, hydroxy C.sub.1 -C.sub.6 alkyl, amino C.sub.1 -C.sub.6 alkyl wherein the amino group is substituted by R.sup.1 and R.sup.2, R.sup.1 and R.sup.2 being independently selected from the group consisting of hydrogen, C.sub.1 -C.sub.6 alkyl, hydroxy C.sub.1 -C.sub.6 alkyl, or R.sup.1 and R.sup.2 taken together with the nitrogen atom to which they are attached forming a 5 or 6 membered saturated ring, or an olefinic group selected from the group consisting of ethylene, propylene and butylene, and X is hydrogen or halogen (preferably chlorine or bromine) surprisingly impart a long lasting intense cosmetically desirable red color to hair. Although the color intensity gradually decreases upon repeated shampooing of the dyed hair, the color tones are advantageously maintained.
Another surprising advantage of these couplers over the prior art couplers is that the dye bath color is identical to the color that will be produced on the hair. There is no color shift as a result of rinsing out the formulation and subsequent shampooing.
Human perspiration generally has a pH of about 5 to 6. Perspiration emanating from the scalp is acidic. Because of acid rain, water supplies are becoming more acidic. An acidic environment can adversely affect dyestuffs that are not acid-resistant. Surprisingly, and advantageously, dyestuffs prepared through use of the 2-substituted-1-naphthol couplers of the present invention are substantially more acid-resistant than dyestuffs prepared through use of the 1-naphthol coupler.